Got this rare used MP3, mate. Yours for $50

SECOND-hand shops have that musty, backstreet magic, with dog-eared albums and well-thumbed books with the owner's name scrawled on the flyleaf.

The goods have such character because they're inherently fragile; they're worn, almost in the process of falling apart. That's why the prices are so reasonable.

But the indestructible CD saw the record industry's attitude to second-hand sales start to wobble. With used CDs being of equal audio quality to new ones, why would the consumer bother buying the shrink-wrapped version?

So when digital media came along, second-hand markets were obliterated with screeds of terms and conditions overriding the "first-sale doctrine" (our right to do whatever we like with things we've bought).

When we pay for MP3s and e-books, we just get a licence; it's permission, not property. We're not allowed to sell them on for a knock-down price, because it would compromise the market for the originals.

But this is changing. At the end of last month, Amazon was granted a patent in the "secondary market for digital goods" that it filed back in 2009. It's clear that Amazon has ambitions to make money from unwanted digital files in much the same way as it does from used goods via Amazon Marketplace.

You can already lend some Kindle e-book purchases to a friend (at which point it neatly disappears from your e-reader) and you can imagine a second-hand market working in a similar way, with your purchase vanishing from your device and popping up in an online store.

Amazon then maintains control over the market by creating a fake scarcity; an OMT (Object Move Threshold) is mentioned in the patent, allowing a "used" MP3 or e-book to be sold once, but only once.

Last weekend, there were reports that the next Xbox console will block second-hand gaming, thanks to activation codes that tether them to the initial user's account. And any attempts by start-ups to create second-hand markets inevitably put them in the legal crosshairs.

Last year, a company called ReDigi set up a second-hand store, coupled with a cloud-based transfer mechanism to move MP3s from one owner to another without actually copying them. It also initiated an artist-syndication scheme, rewarding creators for sales.

Perhaps predictably, lawsuits flew; Capitol Records demanded a fine of £95,000 for every track that ReDigi sold, and that court case rumbles on, with arguments over whether an MP3 can be considered a "material object".

ReDigi continues to trade, and its founders describe the secondary market as "the future of the digital space". But with Amazon's patent awarded, that may be a market entirely controlled by one colossal internet corporation.